| This work was conducted to investigate the characteristics of lead（Pb） in different particle-size fractions of soil aggregates. Soil samples with a range of chemical and physical properties were collected from 22 rural regions of China. Pb in soil aggregates from different particle-size fractions were compared with the its contents in edible amaranth（Amaranthus mangostanus L.） and water spinach（Ipomoea aquatica Forsk） grown on soils in a pot experiment study. Soil aggregates were partitioned into five particle-size fractions：coarse sand（2~0.5 mm）, medium sand（0.5~0.125 mm）, fine sand（0.125~0.05 mm）, silt（0.05~0.002 mm） and clay（<0.002 mm）. It was clear that Pb were not homogeneously distributed over the various particle-size fractions, suggesting that particle size exercises a determining influence on the partitioning of heavy metals. Concentrations of Pb in different fractions ranged from 71.3~2245.4 mg·kg-1. According to particle distribution of the tested soil samples, it can be calculated that concentration proportions of Pb in different particle fractions were 1.98%~22.15% in 2~0.5 mm fraction, 1.98%~22.15% in 0.5~0.25 mm fraction, 3.29%~38.41% in 0.25~0.05 mm fraction, 4.94%~68.17% in 0.05~0.002 mm fraction and 2.30%~56.50% in <0.002 mm fraction. Generally in 14 soils, Pb tended to enriched into finer particle-size fractions, resulting in the most metals accumulate in the clay. In other 8 soils, Pb had bimodal distributions across the particle-size fractions, i.e. the metals tended to accumulate in the clay and one sand fraction of the soils. Correlation analysis showed that pH, organic matter, CEC and amorphous Fe oxides had significant influence on the enrichment index of Pb in different particle-size fractions, and soil aggregates with silt size were found to be the major fraction responsible for Pb adsorption in leafy vegetables. From the soil textural data, it was possible to infer the relative importance of the fractions with respect to their contribution to metal availability. |
